1. Field of the Invention
The present invention relates to a fan motor.
2. Description of the Related Art
Axial fan motors arranged to produce axial air currents by rotating impellers using driving forces of motors are known. The axial fan motors are installed, for example, in household electrical appliances, office automation appliances, transportation equipment, and so on, and are used for the purposes of dispersing heat from electronic components, circulating internal gases, and so on. The structures of such known fan motors are described, for example, in JP-UM-A 04-097496 and WO 2003/015243.
Recent years have seen an increasing demand to use DC motors instead of AC motors in order to improve the efficiency of fan motors. However, an AC/DC converter is required to drive the DC motor in an environment where only an AC power supply is available. Moreover, when an AC/DC converter board is arranged in a wind channel in the fan motor, an air current is interrupted by the AC/DC converter board. This leads to a decrease in the air volume of the fan motor.
JP-UM-A 04-097496 discloses a conventional structure in which an AC/DC converter block is attached to an outside of a housing of a fan motor (see, FIG. 4 of JP-UM-A 04-097496). However, the structure of JP-UM-A 04-097496 causes the AC/DC converter block to partially increase the radial dimension of the fan motor. This structure imposes great constraints on attachment of the fan motor to a target device.
Meanwhile, WO 2003/015243 discloses a conventional structure in which a drive control portion including an AC/DC converter and a control circuit is contained in a base portion of a bearing boss (see FIG. 1 of WO 2003/015243). However, in the case where the AC/DC converter includes a large electronic component, the structure of WO 2003/015243 requires the bearing boss to have a large size. An increased size of the bearing boss restricts the size of a stator and that of blades, and this leads to a decrease in performance of the fan motor.
In recent years, there has been an increased demand for improved efficiency particularly in the field of household electrical appliances. Household electrical appliances such as washing machines and refrigerators are used in high humidity environments or in environments where they are easily exposed to water droplets. Therefore, in the case where the AC/DC converter board is arranged in the fan motor, it is desirable that waterproofness of the board should be taken into consideration.
As a conceivable waterproof structure, the AC/DC converter board may be covered with a resin material, for example. However, in the case where a large electronic component is mounted on a portion of the AC/DC converter board, it is difficult to cover this electronic component and an adjacent area, and a remaining portion of the AC/DC converter board, with a small amount of the resin material.